Spiracle present. Snout and caudal peduncle subconical. Gill membranes joined to isthmus. Mouth transverse. Lower lip with a split in the middle. Barbels not fringed and, in adults, closer to mouth than to tip of the rostrum.
8-25 gill rakers terminated by a single tip.
D: 30-50; A: 22-33 rays.
9-16 dorsal scutes. 24-40 lateral scutes. 8-14 ventral scutes. Scutes are large and stout, radially striated and their surface is covered by small spines. Between the dorsal and lateral scute rows, there are many patches of rhombic denticles.
Colour: in adults it varies from greyish-brown to bluish-black on the dorsum and head. It is paler laterally with hazy dark blotches of variable intensity. Belly white, whitish or yellowish. Pectoral fin yellowish, the other greyish. Scutes dirty to white.

Atlantic coasts from Morocco to northern Norway, including North Sea and Baltic. Northern coasts of Mediterranean and Black Sea. Available data indicate that its reproduction is confined to European waters. A. sturiois a threatened species close to extinction. Two local populations of this species still living on the Iberian littoral: one in Cadiz Bay and the other in the Bay of Biscay (Almaça & Elvira, 2000).

Habitat and Biology

During its stay at the sea, A. sturio is a littoral species limited mainly to estuaries with muddy bottoms; larger specimens occur at depths exceeding 100 m. In the river, younger specimens, 50 to 100 cm in TL, usually stay within a radius of more than 100 Km of the river mouth, and in the sea, the majority are caught at depths of 20 to 50 m.Very little is known about the diet of this species. In the Gironde estuary, juveniles show a strong preference for polychaeta, mainly represented by Heteromastus filiformis, Polyodora sp. and some nereids in lower proportions; crustaceans were the second most abundant group of preys (Brosse et al., 2000). Adult specimens feed on benthic invertebrates (molluscs, polychaeta, isopods and shrimps, as well on small fishes as Ammodytes spp. and gobiids. In the Black Sea, adult specimens feed mainly on fishes, and almost exclusively on Engraulis encrasicolus. Adults do not eat during migration and spawning.A. sturiois an anadromous species. From January to October, with a peak between April to the end of May, mature individuals leave the sea and enter freshwater to spawn. Southern populations begin to appear in the rivers sooner than the northern ones. In the Guadalquivir River, the peak migration of the males occurs two or three weeks before that of the females (Classen, 1944). The distance of the spawning migration seems to be positively correlated with water level, and a distance of 1000 Km or more may be covered during years of high water. Spent fishes immediately return to the sea. In the Gironde River, first spawning migration occur at age of 12 years (males) to 15 years (females). The young sturgeons usually migrate downstream at the age of 2-4 years, usually at the end of summer and in autumn. The occurrence of various age groups of A. sturio, including young specimens, in Lake Ladoga (Berg, 1948) suggests the existence of a non-migrant population in this lake.Spawning occurs in May-June, and juveniles spend 2 years in the river before entering sea (Williot el al., 1997). The spawning sites are stones or gravel.

See A. oxyrhynchus. Specimens younger than about three months have small triangular teeth (Mohr, 1952). Three different species of Acipenseridae, Acipenser sturio , A. naccari and Huso huso (L., 1758) have, in the past, been recorded in the Iberian seas and rivers. However, according to Almaça & Elvira (2000), just one, A. sturiois native to the Iberian Peninsula.